1. Field of the Invention
The present invention relates to an improvement of power-saving capabilities of heating apparatuses and fixing apparatuses, especially to an improvement of power-saving capabilities of image forming apparatuses such as copying machines and printing apparatuses using an electrophotographic method, for example, facsimile machines, and the like.
2. Description of the Related Art
In recent years, the importance of environment issues has been acknowledged and the power-saving capabilities of image forming apparatuses such as copying machines, printing apparatuses, and the like have been improved. In order to improve the power-saving capabilities of these image forming apparatuses, it is effective to lower the temperature of heating units such as a fuser roller and a fuser belt of a fixing apparatus when an image forming apparatus is not feeding paper (in a standby status, for example). However, if the temperature of the heating units is lowered in such a non-paper-feed status, the temperature of the heating units must be raised to a certain temperature again for enabling fixing when the fixing apparatus is used, so that a user must wait until the temperature is raised. As a result, the image forming apparatus requires time to be enabled, so that the usability of such an image forming apparatus is decreased.
In order to avoid this, it is possible to reduce time for raising the temperature of the heating units by supporting electric power supply from an auxiliary power unit to a heat generator of the heating units. There is another method for utilizing electric power in a more effective manner by supporting the electric power supply from the auxiliary power unit to the heat generator of the heating units not only when the temperature of the heating units is raised (in a starting-up status and a return status from an off mode) but also in a paper-feed status.
In this case, “the standby status” refers to a status from an end of an image forming job to a start of the next image forming job, a status from an end of all the image forming jobs to the off mode, and a status (where image forming is enabled) from when the temperature of the heating units is raised to a start of an image forming job, the temperature being raised (reloaded) to such a temperature as to enable image forming after a main power source is turned on or the apparatus is returned from the off mode.
The “off mode” refers to a status where the electric power supply to the heat generator is stopped (in preparation for returning to the next fixing-enabled status) until either one of the following operations (1) and (2) is performed.
(1) A user presses a power source switch (not a main power source switch) of a body of the image forming apparatus.
(2) An external signal such as an image forming start signal or the like is input.
Patent Document 1 discloses an image forming apparatus including a fixing unit configured to heat and fix a toner image, in which the image forming apparatus has an auxiliary energy source for energizing the fixing unit besides a main power source.
Patent Document 2 discloses a fixing apparatus including an electric power adjusting unit for adjusting and supplying electric power to a heat generating unit based on the temperature of a heating unit detected by a temperature detecting unit and residual electric energy of an auxiliary power supply unit detected by a residual electric power detecting unit.
Patent Document 3 discloses a heating apparatus in which a heating unit has a main heat generator for generating heat using electric power supplied from a main power unit and an auxiliary heat generator for generating heat using electric power supplied from an auxiliary power unit. The auxiliary heat generator includes a large-capacity capacitor capable of charging and discharging and a charger charges a capacitor of the auxiliary power unit with electric power supplied from the main power unit. A main switching unit turns on/off electric power supplied from the main power unit to the main heat generator. An auxiliary switching unit turns on/off electric power supplied from the main power unit to the charger. An auxiliary power source switching unit switches between the charge of the auxiliary power unit using the charger and the electric power supply from the auxiliary power unit to the auxiliary heat generator. And a control unit turns on the auxiliary switching unit when the main switching unit is turned off and turns off the auxiliary switching unit when the main switching unit is turned on.
Patent Document 4 discloses a heating apparatus having a heating unit, main power unit, and auxiliary power unit. The heating unit has a heat generator and generates heat using electric power supplied from the main power unit and the auxiliary power unit. The auxiliary power unit has a capacitor. The heating apparatus enables electric power supply from the main power unit and the auxiliary power unit to the heating unit, connects the main power unit to the auxiliary power unit when charging the auxiliary power unit, and supplies electric power from the main power unit to the auxiliary power unit.
Patent Document 1: Japanese Laid-Open Patent Application No. 10-282821
Patent Document 2: Japanese Laid-Open Patent Application No. 2002-278355
Patent Document 3: Japanese Laid-Open Patent Application No. 2003-257590
Patent Document 4: Japanese Laid-Open Patent Application No. 2004-119390
In the above methods, the maximum value of electric energy to be charged in the auxiliary power unit is constant in the standby status and in the preparation for returning to the next fixing-enabled status. In other words, there is only one threshold of control for ending the charge of the auxiliary power unit (a threshold when determining whether the charge of the auxiliary power unit is ended by comparing electric energy charged in the auxiliary power unit with the threshold). When the “return status” is compared with the “paper-feed status”, the “return status” requires more electric energy supplied to the heat generator, so that electric energy required to be supplied to the heat generator upon returning must always be charged in the auxiliary power unit.
Thus, in the paper-feed status, excessive electric power is supplied to the heat generator from the auxiliary power unit. Accordingly, when a small number of pieces of paper are fed repeatedly, using three pieces of paper at one time or using five pieces of paper at one time, for example, it is feared that abnormal temperature rising may be caused in the heating units by supplying excessive electric power to the heat generator from the auxiliary power unit.
In other words, in the return status where the temperature of the heating units is returned to a temperature for enabling fixing from the off mode, it is necessary to supply the heat generator with a large amount of electric energy from the auxiliary power unit in order to raise the temperature of the heating units to the temperature for enabling fixing in a short time. However, the heating units reach sufficient temperature in the standby status, so that it is not necessary to supply the heat generator with a large amount of electric energy from the auxiliary power unit in the paper-feed status following the standby status. Further, there has been a problem in that the heating units are excessively heated and abnormal temperature rising may be caused in the heating units upon repeating the feeding of a small number of pieces of paper if excessive electric power is charged in the auxiliary power unit in the standby status and than discharged from the auxiliary power unit to the heat generator in the paper-feed status.
Moreover, when repeating the feeding of a small number of pieces of paper, if the maximum electric energy charged in the auxiliary power unit in the standby status is limited to a relatively low level so as not to cause the abnormal rising of the temperature of the heating units and the apparatus is returned from the off mode with the maximum electric energy, it is difficult to raise the temperature of the heating units in a short time due to a shortage of electric power on this occasion.